1. Field of the Invention
This invention relates to the field of cementing operations and more specifically to the field of using lightweight foamed cement compositions comprising density reducing additives to service a wellbore.
2. Background of the Invention
Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually recovered by drilling a wellbore down to the subterranean formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe, e.g., casing, is run in the wellbore. The drilling fluid is then usually circulated downward through the interior of the pipe and upward through the annulus, which is located between the exterior of the pipe and the walls of the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass (i.e., sheath) to thereby attach the string of pipe to the walls of the wellbore and seal the annulus. Subsequent secondary cementing operations may also be performed. One example of a secondary cementing operation is squeeze cementing whereby a cement slurry is employed to plug and seal off undesirable flow passages in the cement sheath and/or the casing.
In some environments, cementing operations may need lightweight cement slurries having reduced densities (e.g., a low-density slurry). For instance, cementing across highly depleted zones and weaker formations may need a lightweight cement for sufficient circulation. If the cement cannot be successfully circulated, the desired level of annular fill may not be achieved, and consequently the desired seal may not be achieved. As a result, a large impact on the drilling cost may be experienced and delays in production delivery may occur due to the remedial work.
Lightweight cements are typically prepared by addition of water, microspheres or gas to the cement. Drawbacks to addition of extra water to the cement include reduced efficiency in solidifying of the cement. For instance, the additional water may dilute the cement and thereby extend the time at which the cement may set. Drawbacks to using microspheres include costs associated in adding a sufficient amount of microspheres to reduce the density of the cement to lower than typical densities. Drawbacks to adding gas include excess permeability at high gas concentrations.
Consequently, there is a need in the art for an improved method of preparing a lightweight cement and for cementing with compositions thereof. Other needs include a lightweight cement having improved mechanical properties. In addition, needs in the art include a lightweight cement having a reduced density.